As an apparatus for emitting the liquid, there has so far been known a printer apparatus of the ink jet system in which the ink is emitted via liquid emitting head onto a recording paper sheet, as a support, for recording an image or letters/characters thereon. The printer apparatus, employing this ink jet system, has merits that it is low in running costs and small-sized and lends itself to printing an image as a color image. In the printing apparatus of the ink jet system, inks of plural colors, exemplified by yellow, magenta, cyan and black, are supplied from ink cartridges, containing the inks of these various colors, into e.g. ink liquid chambers of a liquid emitting head.
With this printer apparatus, the inks supplied to for example the ink liquid chambers are thrust by pressure generating devices, such as heating resistors, arranged in the ink liquid chambers, so as to be emitted via small-sized ink emitting ports, that is, so-called nozzles, provided in the ink liquid chambers.
Specifically, the inks in the ink chambers are heated by heating resistors, provided within the ink liquid chambers, to generate air bubbles in the inks on the heating resistors. The inks are emitted from the nozzles under the pressure generated in the ink liquid chambers by the air bubbles, with the so emitted inks being deposited on for example a recording paper sheet, as support, for printing an image or letters/characters thereon.
Among the printer apparatus of the ink jet system, there is a serial printer apparatus in which ink cartridges are mounted in a liquid emitting head unit, and in which the liquid emitting head unit, carrying ink cartridges, is moved along the width of the recording paper sheet, that is, in a direction substantially at right angles to the running direction of the recording paper sheet, for depositing the inks of preset colors on the sheet. There is also a line printer apparatus having a range approximately equal to the width of the recording paper sheet as the ink emitting range. The inks are emitted in a line from nozzles of the liquid emitting head arrayed along the width of the recording paper sheet.
With the serial printer apparatus, the running of the recording paper sheet is stopped as the liquid emitting head unit is being moved in a direction substantially at right angles to the running direction of the recording sheet. The inks are emitted and deposited on the recording paper sheet as the liquid emitting head unit is being moved, with the recording paper sheet being at a standstill. This sequence of operations is repeated. With the line printer apparatus, the liquid emitting head unit is fixed completely, or fixed incompletely to perform minor movements to avoid irregular printing. The liquid emitting head unit emits and deposits the inks linearly on the recording paper sheet which is running continuously.
With the line printer apparatus, in distinction from the serial printer apparatus, the liquid emitting head unit is not moved. Hence, printing may be made at a higher speed with the line printer apparatus than with the serial printer apparatus. Moreover, since it is unnecessary with the line printer apparatus to cause movement of the liquid emitting head unit, each ink cartridge may be larger in size, with the consequence that the ink holding capacity of the ink cartridge may be correspondingly increased. Since the liquid emitting head unit is not moved with the line printing apparatus, the liquid emitting head unit may be provided as one with each ink cartridge, by way of simplifying the constitution.
With the above-described line printer apparatus, the accuracy with which images or letters/characters are printed is affected by the accuracy of timing of deposition of the inks on the running recording paper sheet. More specifically, there is presented such a problem that, with a higher running speed of the recording paper sheet, the images or letters/characters recorded are printed elongated in the running direction of the recording paper sheet, whereas, with a slower running speed of the recording paper sheet, the images or letters/characters recorded are printed contracted in the running direction.
For removing this inconvenience, the line printer apparatus uses e.g. a servo motor, for controlling a motor used for running the recording paper sheet, and the running speed is made constant such as to avoid irregular running speed of the recording paper sheet, thereby controlling the timing of deposition of the inks thereon.
With the use of the servo motor, described above, it is possible to resolve the problem of image elongation or contraction. However, should there be an error as small as several μsec in the timing of ink deposition on the recording paper sheet, the color tone, that is, color density, may become irregular in the running direction of the recording paper sheet. In more detail, should there occur delay of several μsec in the control of the running speed of the recording paper sheet by the servo motor, the color tone becomes dense in the corresponding paper sheet portion.
If the control of the running speed of the recording paper sheet by the servo motor is increased by only a few microns, the color tone becomes thinner in this portion. If the control of the running speed of the recording paper sheet is increased by tens or hundreds of microns, the portions on which no ink has been deposited, that is, so-called white streaks, are generated for extending in a direction substantially perpendicular to the running direction of the recording paper sheet. The irregular color tones or the white streaks, extending in the running direction of the recording paper sheet, appear strongly when printing is made with the gray scale unchanged, as an example.
In the serial printer apparatus, the irregular color tone or the white streaks, occurring in the running direction of the recording paper sheet when printing is carried out as the running of the recording paper sheet is halted, are prevented from being produced by providing a so-called overlap area in a boundary between the previous printing site and the current printing site where the current print area and the previous print area are overlapped with each other. However, even granting that the irregular color tone or white streaks may be prevented from being produced in this serial printer apparatus, such overlap area gives rise to inconveniences such as prolonged time involved in printing, or the increased quantity of the inks used for printing.
In the Japanese laid-Open Patent Publication 2000-185403, it is proposed to tackle this problem by providing a plural number of heating resistors in the ink chambers for facing the ink emitting nozzles of the liquid emitting head so that the heating resistors will be in plane symmetry in a plane containing the nozzle centerlines, and by controlling these heating resistors independently of one another to provide for different heat values of the heating resistors to control the ink emitting directions.
In the liquid emitting head, provided with the plural heating resistors, the respective heating resistors are independently controlled to provide for different heat values of the respective heating resistors to control the directions of emission of the inks from the respective nozzles. Consequently, there is a risk of deterioration of the image quality in case the heat values of the respective heating resistors are inadequate such that the inks cannot be emitted in the desired ink emitting directions.
In more detail, if, in a liquid emitting head 201, shown in FIG. 22, the amounts of the energies supplied to the respective heating resistors 202 are inadequate, the size balance of air bubbles 204, produced in an inks 203 by heating resistors 203 is upset, such that there is a risk that the pressure with which the air bubbles 204 act on the ink 403 is destabilized to cause variable ink emitting directions.
Specifically, with the liquid emitting head 201, if the energies supplied to the respective heating resistors 202 are inadequate, there is a case where the angle of emission θ of an ink droplet i from a nozzle 205 tends to be too small. In this case, in the liquid emitting head 201, the angle of emission θ of an ink droplet i is too small, and hence the ink droplet i touches an edge 205a of the nozzle 205 as the ink droplet is emitted from the nozzle 205, with the result that the ink droplet is emitted in variable directions.
Thus, with the liquid emitting head 201, the point of deposition of the ink droplet i on the major surface of the recording paper sheet P tends to be offset to produce irregular color tone or white streaks to deteriorate the image quality. It is therefore crucial to manage proper control of for example the heat values of the respective heating resistors 202, that is, the quantity of the energies, such as the current, supplied to the respective heating resistors 202 to heat the respective heating resistors 202, in order to emit the ink droplets i from the nozzle 205.